Philadelphia officials asked a state regulator on Thursday to ban the natural-gas drilling technique known as hydraulic fracturing until its environmental effects, especially on drinking water, are studied.

The City Council urged the Delaware River Basin Commission to deny a drilling permit to Stone Energy Corp, a Louisiana-based oil and gas company, or to any other company that wants to use the technique to extract gas in the watershed that supplies the city's drinking water.

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Stone Energy began operations in a protected area of the river basin without the necessary approvals, and now has applied for permits to drill for gas, extracting water it needs from a tributary of the river, the council said.

"We call on the Delaware River Basin Commission to halt Stone Energy's operations, and not approve their application, or any other applications, until a full environmental impact assessment of fracking in the Delaware River Basin has been conducted," the council said in a unanimous resolution.

A spokesman for Stone Energy, Tim O'Leary, said fracking posed no threat to water supplies.

"Stone Energy believes that hydraulic fracturing technologies are a safe and proven method of accessing ample domestic sources of clean natural gas needed by the United States," O'Leary said.

He said the company complied with all local, state and federal regulations governing gas development.

The commission, consisting of representatives from Delaware, New Jersey, New York and Pennsylvania, plus federal officials, is charged with protecting the river over about 330 miles from its headwaters to the Delaware Bay.